The present invention relates to a weave correction system and more particularly to a weave correction system which calculates positional error of a strip of film utilizing anticipated and actual sprocket hole position to register the area being scanned.
Weave correction systems have been fabricated.
British Patent No. 1 412 128 published Oct. 29, 1975 for inventor G. M. Fletcher et al. entitled "Improvements Relating To Telecine Machines", discloses a telecine machine adapted to scan film. The Fletcher et al. telecine machine provides an unblanked video television signal, includes a means to receive the unblanked signal, and a means adapted to detect therefrom film frame edges to generate an output signal. This output signal can be used to correct for errors caused by inaccurate alignment of the film in the camera where error is caused by the misregistration between the negative stock and the print stock due either to mechanical deficiencies in the printer or to differential shrinkage between the two stocks.
In the patent issued to Fletcher, the output signal is compared with a source of field or line frequency pulses and the result of that comparison is applied to this telecine machine to displace the scanning rasters so as to register the raster with the film frames. In the Fletcher patent, the telecine machine does not require the film being corrected to bear any special synchronized markings. A separate optical system as believed required in systems that detect film sprocket holes is not required. The Fletcher system utilizes the rack bars or frame edges between each individual film frame to correct for vertical positional errors caused by camera and printer faults. the Fletcher invention is unaffected by damage to sprocket holes and edit jumps.
This apparatus of the Fletcher et al. patent is also applicable for correction of horizontal movement of the film by detecting the side instead of the top or bottom of the film frame. The horizontal scan can extend over the side edges of the film frame relating the output of an edge detector with line frequency pulses and thereby obtaining representative horizontal positional errors. When detecting horizontal errors, the Fletcher apparatus detects the side of the film frame. When detecting longitudinal or vertical errors, this apparatus conveniently detects the rack bar between the frames.
The Fletcher et al. weave correction system corrects only once a frame for vertical displacement, therefore only correcting for slow moving weave. The Fletcher et al. system does not align the registered film frame to the original registration, the sprocket hole, but rather to the film bar. Further, the Fletcher system does not account for dark film frames which would not easily be differentiated from the film bars. Splices or cuts between film frames affect the film bar placement and would significantly impact the weave correction.
The United Kingdom Patent Application GB 2 213 020 published Feb. 28, 1989 entitled "Correction of Film Instability in Telecine" to inventor Ronald Walter et al., discloses weave correction system using a reference target pattern formed on film. This target pattern is scanned by telecine occupying a predetermined position on the film relative to at least one image frame. The detection of the target pattern and the position to film frame is ascertained and the area scanned by the telecine is adjusted to coincide with the image frame.
This patent to Walter et al., discloses a system wherein electronic and film images which are mixed or superimposed during post-production editing can be corrected for mispositioning of the film frame as caused by irregular sprocket hole pitch, camera, printer or telecine misregistration or velocity errors.
The system as disclosed under GB 2 213 020 utilizes as a registration means a predetermined target pattern printed on the film sprocket hole. In previous weave correction systems, using a sprocket hole had been difficult due to deformed edges of the sprocket hole or sprocket holes clogged with dirt or dust.
The Walter et al. target pattern weave correction method cannot use existing film stock. This system requires specially prepared film stock having reference marks inserted therein to register the film frame.
The U.S. Pat. No. 4,104,680 to David E. Holland, issued Aug. 1, 1978 entitled "Method and Apparatus for Film Weave Correction" discloses a method and apparatus for film weave correction using a moving beam recorder or flying spot scanner wherein the film weave correction apparatus causes the beam to sweep at least once for each frame across a sprocket hole adjacent to the film frame.
A detector behind the film detects the beam recorder crossing the sprocket hole edge and the Holland apparatus compares the time of the edge crossing occurrence with a reference time as driven by the system's horizontal sync pulse.
Based upon this time comparison of the edge crossing versus the reference horizontal pulse, a film weave correction signal is generated. This film weave correction signal is then applied to the horizontal deflection circuitry of the Holland device causing the beam to be shifted in such a manner so that the horizontal position for each scanned frame remains constant with respect to the position of the adjacent sprocket hole rather than with respect to the film edge film guide thereby correcting horizontal film weave.
The apparatus as disclosed in the Holland patent U.S. Pat. No. 4,104,680 in practice does not correct effectively when the sprocket hole is upon a splice, is filled with dust or dirt, or is broken in any way.
The Holland method of weave correction in U.S. Pat. No. 4,104,680 does not correct in the vertical direction. Any change in the size of the raster to accommodate different size film frames detrimentally impact the ability of the system to detect film weave. On film having curved sprocket sides any vertical weave causes an error in the horizontal error obtained.
In U.S. Pat. No. 4,104,680, the manner in which the sprocket hole is scanned from the film frame to the sprocket hole on exposed film could lead to erroneous sprocket hole edge detection.
U.S. Pat. No. 4,823,204 also to David E. Holland, dated Apr. 18, 1989 entitled "Method and Apparatus for Film Weave Correction", discloses a method and apparatus for correction of both horizontal and vertical film weave in connection with a continuous motion moving beam recorder or playback device wherein weave correction is accomplished by scanning the sprocket hole of the film and generating a correction signal to compensate for the film weave. The film weave is corrected by electronic weave correction as opposed to mechanical pin registration.
The weave correction system disclosed in U.S. Pat. No. 4,823,204, scans the sprocket hole in the vertical direction to locate the upper and lower edges of the sprocket hole and then the beam is positioned in the vertical center of the hole for determination of horizontal weave of the film. Then the sprocket hole is scanned in the horizontal direction for determination of the horizontal weave of the film. In a film-to-tape transfer system, the edge position of the sprocket hole is advantageously determined by comparing the actual detected signal with a fast peak detector signal set at 90% of the actual signal level and then provision for setting windows of acceptable weave correction signals, such that if the detected error exceeds the window, the previous weave correction signal which is within the window at the particular time is used.
However, the Holland patent, U.S. Pat. No. 4,823,204 only updates the correction signal once per film frame thereby only correcting for slow moving weave. the problem of fast moving film weave is not addressed by the second patent to Holland.